1. Field of Invention
The present invention relates to a differential pressure sensing device package and a fabricating method therefor. More particularly, the present invention relates to a fabricating method of forming a space on an active region of a differential pressure sensing device in a package and a structure thereof.
2. Related Art
For current micro electromechanical system (MEMS) industry, sensing devices have inherent characteristics of being miniaturized and integrated. However, the overall cost of the device is high, so the application fields and scope of the device is greatly reduced. Under the influence of the personalization and popularity of global communication, it is common that one person holds one or more cell phone(s). Due to the communication requirements between parents and children, even the pupils that just enter elementary schools hold the cell phones, so the cell phone-consuming age group is going to fall into the group of children less than 10 years old, and thus the demand for the cell phone is greatly increased. A research report based on topology of September 2005 has figured out that the total shipping number of the cell phone in 2005 all over the world is approximately 0.76 billion, and the number of the cell phone users goes up to 1.685 billion. The report also predicts that in 2009, the number of the cell phone users all over the world will go up to 2.236 billion. Therefore, the scale of the application market of the cell phone is quite large.
For the product attribute and design concept of cell phone, in addition to conversation and basic functions, the cell phone has additional functions, such as image communication, wireless data transmission, network connection, time display, alarm clock, notebook, world time zone, e-mail, personal secretary, GPS navigation, satellite positioning and searching, electronic map, wireless remote control, MP3 music, real-time image, digital photographing, digital program receiving, horizontal elevation, monitor alarm, digital game, radio, memory, etc. Due to the expansion requirement of the function, the number of the elements and the possibility of the integration of the elements in the cell phone are greatly increased. Unfortunately, impelled by the light in weight and small in size” requirement, the volume of the cell phone cannot be increased with the increase of the functions of the cell phone. Further, due to the sale point of light and chic, the size of the cell phone may be limited in a certain scope, and even the profile is further reduced. On the other hand, the cell phone is a common product in the global market, so the overall cost will be limited in a reasonable scope, and cannot be sold at high unit price like high-tech instruments or fittings. The overall cost of the elements installed in the cell phone will challenge the design. Therefore, the low cost and consistent production has become a design rule and principle for the elements in the cell phone, and it is the trend of the technical research.
In addition, for future cell phones, the requirements for sensing the environment information, such as temperature, humidity, volatile organic compound (VOC), carbon oxide toxic gas, ultraviolet strength, content of oxygen in the air, content of ammonia in the air, will be integrated into the cell phones. Therefore, it is necessary to develop a miniaturized sensing mechanism. The differential pressure sensing device is the only optimal possible approach at present. Currently, in cell phones, a certain amount of elements has adopt MEMS elements, such as microphones of speakers, micro-gyros for game effect, CCDs for photographing, and the possible sensing devices of the future cell phones, such that the MEMS sensing device plays an important role in the future cell phones. The size of the sensing device after packaged is required to be miniaturized to the maximum extent.
In the cost architecture of the MEMS sensing device, the package cost usually takes up 70% to 80% of the overall cost of the sensing device, so in order to reduce the cost of the sensing device, the package cost must be firstly considered, and is also a most effective and important direction of improvement.
For the common sensing device, in order to make the sensing mechanism on the device surface communicate with the outside atmosphere after the device is packaged to achieve the objective of sensing the environment, it is necessary to form a channel above the sensing region of the surface of the sensing device. In a known sensing device package, for example, disclosed in U.S. Pat. No. 6,379,988 B1, referring to FIG. 1A, a differential pressure sensing device package 10 is provided. Before the molding of the sensing device 11, a sacrificial protection layer 13 is covered on the surface of the sensing device in order to protect a micro-sensing or stopping structure 12 of the upper surface of the sensing device 11. The sacrificial protection layer 13 after the molding process is entirely embodied in the molding material 14, so it is necessary to open a window above the micro-sensing or stopping structure 12. The method of opening the window is as shown in FIGS. 1B and 1C, in which the spray etching using different strong acid is performed twice. Firstly, a first pad 15 is loaded on the molding material 14 to confine the region of the acid spray process. Then, a first strong acid 16 is sprayed for an appropriate time controlled for acid etching, so as to etch and remove the molding material 14 in contact with the first strong acid 16, such that the sacrificial protection layer 13 is exposed. Then, a second pad 17 is loaded on the first opening area of the molding material 14, and a second strong acid 18 is sprayed for an appropriate controlled time for acid etching, so as to etch and remove the sacrificial protection layer 13 to release the micro-sensing or stopping structure 12 of the sensing device 11 to contact the atmosphere.
However, the process of the differential sensing device package 10 of the conventional art has obvious defects. Firstly, in consideration of the method for opening the window, the conventional art adopts the strong acid spray etching technique. By the use of different strong acid materials and different pad shapes, the first layer of molding material 14 and the second layer of sacrificial protection layer 13 are opened. The strong acid process needs additional acid etching pads, and it is not easy to control the acid etching parameters, such that the yield is not high and also the problems of industrial safety and environment pollution exist. The strong acid process is used to process one by one, and the throughput is quite low. Further, in the conventional art, the sacrificial protection layer 13 must be used to entirely cover the surface and then expose the wire bonding area, so the complex patterns and processes will affect the yield of the wire bonding process.